The present invention relates to a damper and, more particularly, to a remotely trippable and resettable damper having improved sensing and actuation capabilities.
One damper commonly employed in the art is known as a combination fire and smoke damper. These dampers are typically installed at various locations in a building's ventilation system to prevent circulation of fire and smoke throughout the building during a fire condition. These prior art dampers generally include a damper blade(s) that can be maintained in either an open or a retracted position during normal operating conditions. Each of these dampers must also be capable of sensing a fire condition in the building and, thereafter, releasing or actuating the damper blade(s) to allow such blade(s) to travel to the closed position to provide a wall-like barrier in the ventilation system.
Early dampers, which typically were concerned only with limiting travel of fire through a ventilation system, included an accordion-type blade maintained in a folded state at the top of the damper. For example, U.S. Pat. No. 3,580,321 includes a blade that is maintained in a closure sealed by a hinged door. In a fire condition, the door is opened and the blade falls downward out of the closure due to gravity, thereby limiting travel of fire through the ventilation system.
However, there were several disadvantages with these early dampers. For example, many of them required that the damper blade be manually reset. This made it difficult for emergency personal to ventilate the building after the fire-fighting period. In particular, it is often desirable to be able to control the flow of smoke resulting from a fire in a building. The early fire dampers restricted the fire fighter's ability to accomplish this task because these early dampers, once closed, remained closed until after the fire was extinguished and the damper manually reset.
These early fire dampers also lacked the ability to effectively seal the ventilation duct during a fire condition. Because they operated on a gravity basis, they could not be designed in too tight a manner. In addition, early fire dampers lacked a fail-safe closed mode (i.e., a mode in which the damper blade automatically travels to the closed position in the event of a system malfunction).
Although resettable folding blade dampers are now known in the art, more recent dampers are designed with a rotatable damper blade(s), rather than a plurality of foldable blades. These newer dampers offer several advantages over the folding blade design. Particularly, a tighter seal can be accomplished and maintained with a rotatable-type damper. These same dampers are also more readily adaptable for inclusion of a fail-safe mode.
Rotatable-type dampers are typically designed with a single or a plurality of blades rotatably mounted on or connected to a shaft passing transversely across the damper. When the blades are maintained in an open position (i.e., the blades are aligned parallel to one another), air is free to travel through the ventilation system. However, when the blades are rotated to a closed position, the damper effectively seals off the ventilation system.
One such rotatable-blade damper is disclosed in U.S. Pat. No. 4,301,569. The '569 damper includes a plurality of rotatably-mounted damper blades interconnected by means of a common linkage. The linkage is pivotably connected to a rotatable plate-like member upon which a bi-metallic fire link is mounted. This link couples the plate-like member to a control shaft which is employed to maintain the damper blades in an open position during normal operating conditions. During a fire condition, the bi-metallic strip in the fire link expands outwardly, thereby decoupling the plate-like member from the control shaft. A biasing spring, which is associated with the plate-like member, then drives the member, along with the connected linkage and damper blades, to the closed position.
The structure and operation of the '569 damper produces several disadvantages. For example, the fire link employed in the '569 damper functions as both the fire-sensing means and the release means. Specifically, as the bi-metallic strip is heated, it expands outwardly, thereby decoupling the plate-like member from the control shaft. However, to decouple these components, the bi-metallic strip must overcome the strong friction force imparted on the components by the biasing spring. Because the bi-metallic strip has only a limited expansion force, it may be difficult for such strip to overcome the friction force and release the plate-like member from the control shaft. In addition, if the fire link remains unused for a period of time, factors such as rust, dirt and dust increase the likelihood that the bi-metallic strip will be unable to release the plate-like member from the control shaft. At the minimum, the temperature characteristics of the link will be affected and the damper will not be tripped at the appropriate predetermined temperature.
The '569 damper has a second significant disadvantage. Because the damper employs a bi-metallic strip to both sense a fire condition and release the damper blades, the positioning of the fire sensor is, by necessity, limited to a location on or adjacent the actuating mechanism of the damper. It may prove beneficial, however, to locate the fire sensor at a distance from the damper, or even to employ a plurality of sensors that would improve the sensitivity and reliability of the system.
A third disadvantage associated with the design of the '569 damper concerns the necessity of the actuating mechanism (i.e., the fire-link, plate-like member, etc.) to be located inside the ventilation system. As mentioned, the bimetallic strip, which must be positioned in the ventilation system in order to sense a fire condition, is an integral part of the actuating mechanism. Hence, it is not possible to locate such mechanism outside the ventilation system, (e.g., to avoid exposure to high temperatures) as may be desired in particular installations.
Although the above discussion pertains to combination fire and smoke dampers, dampers are employed in other applications such as the isolation of hazardous gases accidently released in a laboratory facility. Dampers may also be employed to isolate certain regions of a building in preparation for the release of an inert gas such as halon. The dampers employed in these applications suffer from the same drawbacks associated with fire and smoke dampers. In short, a damper design such as the one employed by the '569 device, which relies on a heat-sensitive bimetallic release mechanism, is unable to be utilized in these other applications.